1. Field of the Invention
The present invention relates to a tape loading apparatus for use in a magnetic recording/reproduction apparatus, such as a video tape recorder (VTR).
2. Description of the Related Art
Recently, recording density has increased as magnetic recording/reproduction apparatuses, such as VTRs, etc. , have become digital and miniaturized. As a result, there is a demand for an improved precision tape running system. Of course, a high degree of precision is required for a tape loading apparatus. For audiovisual products, there is a trend toward reduced size and cost. The same is true of magnetic recording/reproduction apparatuses, such as VTRs, etc.
A conventional tape loading apparatus will be described below. For example, Japanese Patent No. 2701575 discloses a conventional tape loading apparatus. FIGS. 5, 6 and 7A through 7D illustrate this conventional tape loading apparatus for use in a VTR. These figures are based on FIGS. 3, 4, 5 and 15 of Japanese Patent No. 2701575. FIGS. 8 and 9 illustrates a tape guide post mechanism for a conventional tape loading apparatus, such figures being based on FIGS. 4 and 5 of Japanese Patent No. 2789838, respectively. For sake of simplicity, the “boat reference surface” and “reference surface” referred to in Japanese Patent No. 2701575 with respect to FIG. 15, are referred to differently herein as the “boat-side reference surface” and “base-side reference surface” in relation to FIG. 7.
In FIG. 5, reference numeral 52 indicates a cassette, 63 indicates a magnetic tape, and 69 indicates a rotary head cylinder. Reference numeral 58 indicates a feed side loading roller post serving as a tape guide post, which guides the running of the magnetic tape 63. Reference numeral 64 indicates a feed side boat serving as a carrier which carries the feed side loading roller post 58 and an inclined post 66, and draws the magnetic tape 63 present within the cassette 52. Other than these tape guide posts, a plurality of tape guide posts (representing a tape guide post group), such as a tension post 59, take-up side loading posts 60 and 61, and an auxiliary guide post 73 are also used to withdraw the magnetic tape 63 present within the cassette 52. Therefore, a predetermined tape running system is established, so that sound or visual images can be recorded to or reproduced from the magnetic tape 63.
Referring to FIGS. 5 and 6, the magnetic tape 63 withdrawn out of the feed side reel 53 is wrapped about the feed side loading roller post 58 via tape guide posts 59, 76 and 66. Thereafter, the magnetic tape 63 is wrapped about the rotary head cylinder 69, and then about the take-up side loading post 60. The magnetic tape 63 reaches a take-up side reel 64 via a predetermined tape running system. FIG. 6 is a perspective view showing only parts which are associated with the tape running system in the state shown in FIG. 5.
Referring to FIGS. 7A to 7D, reference numeral 51 indicates a chassis as a base, 86 indicates a stopper, 53 indicates a drive shaft. Three boat-side reference surfaces are provided on the rear side of the feed side boat 64. FIGS. 8 and 9 are diagrams showing the mechanism of the tape guide posts and their vicinity of the conventional tape loading apparatus. The arrangement shown in FIGS. 8 and 9 is a typical mechanism of adjusting the height of conventional tape guide posts.
In FIGS. 8 and 9, reference numeral 65 indicates a take-up side boat serving as a carrier, 68 indicates a pipe having an internal thread portion 68a and cylinder portion 68b, which is press-fit onto the take-up side boat 65. Reference numeral 60 indicates a take-up side loading post comprising a roller 60a, a shaft 66, a roller holding member 67, and an upper flange 60b. The roller holding member 67 and the upper flange 60b are press-fit onto the shaft 66. The roller 60a is rotatably supported at an upper portion 66a of the shaft 66 while the upper limit of the position of the roller 60a is defined by the upper flange 60b and the lower limit of the position of the roller 60a is defined by the roller holding member 67. The upper flange 60b and the roller holding member 67 also keep the running of the magnetic tape within the upper and lower limits. The roller holding member 67 has an external thread portion 67a, which engages the internal thread portion 68a of the pipe 68. Reference numeral 80 is a screw which engages an internal thread portion provided in a screw hole 81 of the pipe 68. The tip of the screw 80 presses the circumferential surface of a lower portion 66b of the shaft 66. A hexagonal hollow or slot portion is provided on the top portion of the upper flange 60b, which is engaged with a tool, such as a driver etc. , to rotate the upper flange 60b. The rotation of the upper flange 60b causes the shaft 66 and the roller holding member 67 to rotate together.
It should be noted that although the upper flange 60b, the roller 60a, the external thread portion 67a, the internal thread portion 68a, the cylinder portion 68b, the upper portion 66a, and the lower portion 66b are not designated in FIG. 5 of Japanese Patent No. 2789838, these names are added in FIG. 9 for the sake of clarification and convenience. Japanese Patent No. 2701575 does not describe the mechanism of adjusting the height of a tape guide post in the loading mechanism. In fact, the height adjusting mechanism as shown in FIG. 5 of Japanese Patent No. 2789838 is generally incorporated into the loading mechanism. Hereinafter, it is assumed that the height adjusting mechanism as shown in FIG. 5 of Japanese Patent No. 2789838 is incorporated into the loading mechanism of Japanese Patent No. 2701575.
The operation of the thus-constructed conventional tape loading apparatus will be described. The feed side boat 64 is in a state shown in FIG. 7A and 7B when the loading operation has been completed. Specifically, the drive shaft 53 biases the feed side boat 64 to the left. This biasing force causes the feed side boat 64 to contact and press the stopper 86. The feed side boat 64 experiences a reaction force from the stopper 86 in a direction indicated by arrow F (FIG. 7D). As a result, the three boat-side reference surfaces on the rear side of the feed side boat 64 are caused to press the base-side reference surface of the chassis 51, so that the feed side boat 64 is tightly fitted with the base-side reference surface. Therefore, the height of the feed side boat 64 is determined with a high degree of precision only after the feed side boat 64 is in such a state. In this case, the inclination of the feed side boat 64 is also determined with a high degree of precision. As a result, the height and inclination of the feed side loading roller post 58 (tape guide post) carried by the feed side boat 64 are determined with a high degree of precision.
For the current VTR, the width of a track recorded in a magnetic tape is 5 to 20 μm. Therefore, a magnetic tape wrapped about a rotary head cylinder requires a precision of 1 to 2 μm with respect to their relative positions. Therefore, the height precision and inclination of a tape guide post placed near the rotary head cylinder are very important. Specifically, referring to FIG. 6, the precision of the position and inclination of the feed side loading roller post 58 and the take-up side loading roller post 60 is particularly important. The height and inclination of these tape guide posts require a precision of several μm and about 0.2° to 0.5°, respectively. In the future, a higher degree of precision is required as recording density is increased. Needless to say, the greater the height and inclination precisions, the better the quality.
In FIGS. 7A to 7D, variations in the height of the base-side reference surfaces and the height of the feed side loading roller post 58 with respect to the feed side boat 64 are about 10 to 50 μm. Therefore, it is difficult to guarantee a height precision of several μm by simply assembling parts. To avoid this difficulty, in the arrangement shown in FIGS. 8 and 9, for example, the height of the tape guide post 60 is adjusted to obtain required precision by rotating the tape guide post 60, with the hollow portion of the upper flange 60b of the tape guide post 60 being engaged and rotated by a driver.
In order to maintain the precision after the height adjustment, there must not be a play in the vertical direction between the external thread portion 67a of the roller holding member 67 and the internal thread portion 68a of the pipe 68 when they are engaged with each other in FIG. 9. The height of the tape guide posts must not be changed due to vibration, repetition of use, aging, etc. In the arrangement shown in FIG. 9, the screw 80 is laterally driven to press the lower portion 66b of the shaft 66 against the internal wall surface of the cylinder portion 68b of the pipe 68, so that the tape guide post 60 is secured to a carrier (in this case, the take-up side boat 65). Therefore, the height of the tape guide post 60 is prevented from being deviated from the adjusted state.
Referring again to FIG. 7B, the precision of the inclination of the tape guide post 58 is the sum of the inclination precision of the base reference surfaces and the inclination precision of the tape guide post 58 with respect to the boat-side reference surfaces. Therefore, in order to ensure the above-described inclination precision of 0.2° to 0.5°, the inclination precision of the base-side reference surface is about 0.1° to 0.3° and the inclination precision of the tape guide post 58 with respect to the boat-side reference surface is about 0.1° to 0.3°, which is a typical specification for this arrangement. Therefore, typically, the cylindricity of the internal wall surface of the cylinder portion 68b (FIG. 9) of the pipe 68 is about 1 to 3 μm, and the inclination precision of the cylinder portion 68b with respect to the boat-side reference surface is about 0.1° to 0.3°.
There are, however, the following problems with the above-described conventional arrangement. Variations in the inclination of a tape guide post with respect to a base is basically the sum of variations of the inclination of a base-side reference surface and variations in the inclination of the tape guide post with respect to the boat reference surface. High precision machining is required for the base reference surface and the cylinder portion of a pipe with respect to the boat reference surface. Such high precision requires the state of the art machining technology, which leads to an increase in cost for parts. The term “machining” as used herein refers to industrial machining, such as cutting, alloy sintering, resin molding, etc.
The supporting portion of the tape guide post 60 (the lower portion 66b of the shaft 66 in the arrangement shown in FIG. 9) needs to be disposed along the internal wall surface of the cylinder portion 68b of the pipe 68 with a high degree of precision. From this reason, the length of the engagement of the pipe 68 and the tape guide post 60 cannot be smaller than a predetermined size. Therefore, a problem arises in miniaturization.
The carriers 64 and 65 must be made of a material capable of being generally machined with a high degree of precision, such as cast metals (e. g. , zinc die-cast or aluminum die-cast) or super engineering plastics (e. g. , PPS, etc. ), leading to problems such as the costs for materials for parts and molding the materials are high.
In the arrangement of FIG. 7, there is substantially no means for adjusting the inclination of the tape guide post 58 after assembly. Parts having insufficient inclination precision are abandoned, resulting in low yield and high cost.
Adequate spacing for the screws on the tape guide post 58 and the carrier side for use in the height adjusting mechanism is required, thereby making it difficult to design a small carrier and tape guide post. As a result, it is difficult to obtain a small mechanism.
The screw on the tape guide post 58 (the external thread portion 67a of the roller holding member 67 in FIG. 9) and the screw on the carrier side (the internal thread portion 68a of the pipe 68) for use in the height adjusting mechanism are difficult to be produced by component rolling due to their shape constraints. Therefore, such screws have to be shaped by thread cutting, leading to an increase in cost.
It is impossible to manufacture a tape guide post such that the lower portion of the tape guide post supported by a carrier is perfectly in parallel to the tape guide portion of the tape guide post. Specifically, in FIG. 9, the lower portion 66b and the upper portion 66a of the shaft 66 are not perfectly in a straight line. Therefore, the roller 60a supported by the upper portion 66a cannot be manufactured to be perfectly in parallel to the lower portion 66b. Therefore, when a tape guide post is rotated in adjusting the height of the tape guide post, such a slight angle difference causes the tape guide portion to be precessed with respect to the carrier. Therefore, the height adjustment changes the inclination of the tape guide portion with respect to the base, thereby reducing the inclination precision of the tape guide post.
A lateral screw is required for removing play between a tape guide post and a carrier (screw 80 in FIG. 9). Therefore, the number of parts is increased, tapping is required, tightening a screw is required, the number of steps is thus increased, etc. , thereby increasing cost.
The height of a tape guidepost is adjusted by rotating the tape guide post. Therefore, a hollow portion with which a driver or the like is engaged to rotate the tape guide post is generally provided at the upper flange portion thereof. Thus, a slot or hexagonal hollow portion is provided at the upper flange portion, thereby increasing cost (in FIG. 9, no hollow portion is shown at the upper flange portion, but a hollow portion is generally provided at the upper flange portion so as to rotate the tape guide post).
The carrier and the tape guide post are not perfectly rigid bodies. Even if there is no play in the engagement between the carrier and the tape guide post, the tension of a magnetic tape causes slight elastic deformation of the carrier and the tape guide post. Therefore, fluctuation of tape tension slightly modifies the inclination and height of a tape guide post, whereby the inclination and height of the tape guide post become unstable.
When a carrier is made of zinc die-cast or resin which is easy to shape, the carrier is slightly deformed over time, particularly under high temperature. In this case, the inclination and height of a tape guide post is slightly changed, thereby reducing the inclination and height precisions of the tape guide post. A thicker carrier is required in order to minimize such variations, but the larger size inhibits miniaturization.